Hitherto masks have been widely used in medical practice for the application of gases or, more recently, for use with nebulization, that is the application of drugs to a pateint by means of an aerosol produced by a flow of gas, the aerosol and drug being breathed in through a face mask.
For hygienic reasons, it is preferred to use a new mask for each treatment. Thus masks have increasingly become considered to be disposable items. Hitherto, however, mask assemblies have comprised a face mask of generally plastics material, a separately formed nozzle for connecting to the supply of gas, and a retaining strap generally in the form of a separate woven elastic strap connected to the mask itself by various means including knots in the woven elastic and holes in the mask. Various configurations of face mask have been tried but they suffer from the disadvantage of being relatively costly items, and in particular generally being more costly than is desirable in a disposable item.
In particular the cost of the mask is increased because the strap for holding the mask in contact with the face is a separately produced item and manual labour is required to assemble the strap and the mask whether the strap is connected to the mask simply by passing the strap through the hole in the mask and tying a knot there behind or by other clip means which typically comprise metal rings. An example of such a mask is disclosed in British Patent Specification No. 920216 in which the mask is retained to the patients face by means of tapes or elastic bands 15 which are attached at spaced points to the periphery of the mask and are then passed around the back of the patient's head. The mask in British Specification No. 920216 is intended to cover the nose and mouth of the patient and includes a gas delivery pipe 11 in addition to the tapes 15. It will be understood that the mask comprises a number of other separate parts, the gas delivery pipe 11, the collar 19, the wire 14 and the skirt portion 21.
The applicants have also had drawn to their attention French Specification No. 8482268 which shows a gas mask moulded in a resilient material (rubber). There are considerable difficulties in moulding rubber at high speed which is necessary if the mask is to be produced cheaply. Furthermore, the moulding arrangement disclosed in the French Specification No. 848268 would not lend itself to moulding with a suitable modern plastics material. If a resilient elastic material such as rubber is used for a mask, then because of its resiliency it has to be of substantial thickness to be self supporting and able to maintain its shape. In particular, the cup shape part covering the nose and mouth must be fairly thick to be sufficiently rigid to maintain its shape when the patient breathes in. This is very wasteful of material and makes the mask very expensive. For this reason, a more rigid plastics material must be used which will maintain its shape. Such a material is substantially non-elastic and it is therefore not possible to mould it in the way shown in the French patent specification. It is only by the use of such a material that a sufficiently rigid mask can be made which is of thin-wall section elastic. Furthermore, the mask in the French specification is incomplete requiring the addition of glass or other material for the eye holes.